Field of the Invention
The invention relates to liquid discharge heads that are driven by electric signals, and more particularly to a liquid discharge head to which an electric signal is transmitted via a plurality of electrical components joined to the liquid discharge head.
Description of the Related Art
In a common liquid discharge head of the related art, an electric signal is supplied to a discharge element from the outside via a plurality of electrical components (a wiring substrate and a wiring tape). Here, the plurality of electrical components need to be joined together with a resistance that is equal to or lower than a predetermined value in order to suppress degradation of signal integrity and loss of electric energy. However, the size of the joining region where the electrical components are joined together increases as the size of the electrical components increases, and it is difficult to join the electrical components together in such a manner that the resistance is equal to or lower than a predetermined value over the entire joining region.
When a failure occurs in a joint portion between the electrical components, in the case where an electric signal cannot be transmitted to the discharge element due to deterioration of the signal integrity, the failure can be detected as an initial discharge failure during inspection prior to shipping. However, in the case of a joint failure such as one that causes only loss of electric energy, when the loss is small, there is a possibility that the failure will not be detected as a discharge failure during the inspection prior to shipping, and that the failure will become notable along with aging of a product (e.g., in the case where the discharge element is a heater, a burn mark on a surface of the heater and the like) during the use of the product. In order to avoid bringing to market a liquid discharge head in which such a discharge failure will possibly occur, there is a need to ensure the quality of shipped goods by inspecting and managing the state of the joints between a plurality of electrical components by using resistance values in the manufacturing process.
Japanese Unexamined Utility Model Registration Application Publication No. 63-135174 discloses a flexible joining conductor such as a flexible printed circuit board or a flat cable that has a diagnostic function for determining breakage. A dummy conductor is disposed at a side end of the flexible joining conductor, and the flexible joining conductor includes a breakage detection unit that detects breakage of the dummy conductor. Accordingly, the flexible joining conductor is capable of detecting beforehand that a failure, which has occurred therein, has progressed and is capable of taking appropriate measures against the failure before a signal line breaks.
However, in the diagnostic function for determining breakage described in Japanese Unexamined Utility Model Registration Application Publication No. 63-135174, Boolean determination having two results, which are a conducting state and a non-conducting state, is performed, and thus, a state cannot be detected where the resistance is equal to or higher than a predetermined value, despite conduction, and as a result, inspection of a joint portion cannot be performed with high accuracy.